The present invention generally relates to communication signal processing and particularly relates to demodulating such signals.
Accurate recovery of the originally transmitted information from a received communication signal presents significant challenges in the context of wireless communication systems, such as wireless Local Area Networks (LANs) and, in particular, mobile radio networks. Mobile communication networks for example represent particularly challenging environments, because of the rapidly fading propagation channels, multi-user interference, etc.
In a common approach to information recovery, received signals are demodulated based on comparing sampled portions of the incoming signal to hypotheses representing possible values of the received signal. Such approaches suffer because the comparison is polluted by unaccounted for interference and thus it is difficult to know whether comparison results reflect good or bad hypotheses, or simply reflect the effects of unaccounted for noise. Further, particularly in the context of complex transmit signal modulation constellations, the number of candidate signals that must be evaluated to identify the received signal becomes prohibitively large with respect to the amount of time normally available to process signals in real or near real-time.
One alternative to the above approach to demodulation involves so-called joint detection, wherein the receiver jointly detects and demodulates desired and interfering signals together. With the signal information thus gained for the interferer signal, suppression of the interference arising from it is a relatively straightforward proposition. However, the niceties gained in interference suppression are more than offset by the attendant increase in demodulation complexity arising from the joint detection itself.